The filter of a filter cigarette has a rod-like filter material and a wrapping material that envelops the filter material. One of the wrapping materials is a filter having a plurality of perforations. When the filter cigarette with a filter having perforations is smoked, air flows into the filter through the perforations, which dilutes smoke from the cigarette. As a result, nicotine and tar contained in the smoke are reduced, so that the smoker can enjoy a mild flavor.
The ratio of an air amount flowing in from the perforations to an amount of the smoke drawn by the smoker is called filter ventilation (hereinafter also simply referred to as VF). As for the above-mentioned filter cigarettes, if VF is not fixed constant for each cigarette, the cigarettes do not have a uniform flavor and vary in their qualities.
The International Organization for Standardization defines a method of measuring VF, which is carried out by a measurement standard. This measurement standard is used in manufacturing plants of filter cigarettes. More specifically, filter cigarettes are pulled out of the tobacco-manufacturing machine at a constant rate, and the VF of the pulled-out filter cigarettes is measured by the measurement standard. In short, only some of the manufactured filter cigarettes are subjected to the extraction and the inspection of VF.
The method of measuring VF, which is compliant with the ISO, however, is complicated because it is troublesome to install the measurement standard in the tobacco-manufacturing machine. Even if the measurement standard can be installed in the tobacco-manufacturing machine, it takes a lot of time to inspect the VF of each filter cigarette. Therefore, it is difficult to conduct the inspection of all the manufactured filter cigarettes by this measuring method.
The measurement standard is also used in the inspection of undesired holes made in wrapping paper. As to a filter cigarette having great VF, however, an air amount flowing in through perforations is relatively greater than the air amount flowing in through the holes made in the wrapping paper. This makes it difficult to detect the holes made in the wrapping paper without fail by using the measurement standard.
The tobacco-manufacturing machine disclosed in Japanese Patent No. 3190132 has an inspection apparatus for inspecting not VF but total ventilation (hereinafter also simply referred to as VT) as a control index for a nicotine and tar amount. The VT is the ratio of an air amount flowing in from the perforations of wrapping paper and filter of the cigarette to an amount of the smoke drawn by the smoker.
However, this well-known inspection apparatus is not capable of directly inspecting the VF, and not capable of credibly control the nicotine and tar amount of filter cigarettes.